1. Field of the Invention
The present invention relates to a vibrating gyroscope, and more particularly to, for instance, a vibrating gyroscope used to detect rotational angular velocity for preventing shaking in a camera.
2. Description of the Related Art
FIG. 1 is a perspective view of an example of a conventional vibrating gyroscope. The vibrating gyroscope 1 comprises for instance a vibrator 2 in the shape of a rod having a triangular cross section. Piezoelectric elements 3a, 3b, and 3c are provided on the three side faces of the vibrator 2. To use the vibrating gyroscope 1, as for instance shown in FIG. 2, an oscillation circuit 4 is connected between the piezoelectric elements 3a, 3b, and 3c. Moreover, the piezoelectric elements 3a and 3b connect to a detection circuit 5. The detection circuit 5 comprises a differential amplifier, a synchronous detection circuit, a smoothing circuit, a dc amplifier circuit, and the like.
In this vibrating gyroscope 1, the output signal of the piezoelectric element 3c feeds back to the oscillation circuit 4. In the oscillation circuit 4, the fed back signal is amplified, and further phase-adjusted to produce an excitation signal. The excitation signal obtained in this manner is applied to the piezoelectric elements 3a and 3b. As a consequence, the vibrator 2 vibrates under a bending mode in a direction at a right angle to the face upon which the piezoelectric element 3c is located. In this state, the bending state of the piezoelectric elements 3a and 3b is the same, and their output signals are the same. Therefore, no signal is output from the differential amplifier of the detection circuit 5. When the vibrator 2 is vibrating under a bending mode, and rotates around the axis of the vibrator 2, the Coriolis force changes the vibration direction of the vibrator 2. Consequently, a difference is created between the signals output from the piezoelectric elements 3a and 3b, and the differential amplifier outputs a signal. This signal is detected by the synchronous detection circuit, smoothed by the smoothing circuit, and amplified by the dc amplifier circuit. Therefore, it is possible to detect the rotation angular velocity by measuring the output signal of the detection circuit 5.
Furthermore, as shown in FIG. 3, a vibrator comprising two piezoelectric substrates 6a and 6b joined together may be constructed as the vibrating gyroscope 9. As shown by the arrows in FIG. 3, these piezoelectric substrates 6a and 6b are polarized in reverse directions. In this case, electrodes 7a and 7b are provided on one face side of the vibrator 2 extending in the length direction thereof, and an electrode 8 is provided entirely over the other face side of the vibrator. In such a vibrating gyroscope 9, it is possible to detect the rotation angular velocity using the circuit shown in FIG. 2.
However, with these vibrating gyroscopes, it is only possible to detect rotation angular velocity around the axis of the vibrator, and it is only possible to detect angular velocity in one direction. Therefore, in order to detect the rotation angular velocity in two directions, two vibrating gyroscopes must be used, and two oscillator circuits must be provided to excite these vibrating gyroscopes. Such an oscillator circuit is expensive, raising the cost of detecting angular velocity in multiple directions.
For the forgoing reasons, there is a need for a vibrating gyroscope capable of detecting angular velocity in two directions with one element.
The present invention is directed to a vibrating gyroscope that satisfies this need. The vibrating gyroscope includes: a support; four vibrating arms, four weights and excitation and detection elements. Each of the four vibrating arms has a first end and a second end in a longitudinal direction, and the four vibrating arms are fixed to the support at the respective first ends in the longitudinal direction such that four vibrating arms are radially arranged in a single plane with the adjacent arms making an angle of about 90 degrees. The four weights are fixed to the support so as to be arranged radially between the respective adjacent vibrating arms. The excitation and detection elements vibrate the vibrating arms under a bending mode within the single plane and output signals generated by the vibration of the vibrating arms.
The excitation and detection elements cause the four vibrating arms to vibrate under a bending mode around the center member within the plane in which they are provided. At this time, since adjacent vibrating arms are arranged so as to intersect each other at right angles, the vibration of the vibrating arms acts as a force in the rotation direction on the entire structure. However, since the weights are provided between the vibrating arms, the weights vibrate in the reverse direction to the vibration direction of the vibrating arms, whereby a force acts in a direction to cancel the rotational force of the vibrating arms. When the vibrating gyroscope rotates around the axis of the vibrating arms, a Coriolis force changes the vibration direction of the vibrating arms, and a signal in correspondence with the Coriolis force is output from the excitation and detection element. Here, since the four vibrating arms are arranged so as to intersect at right angles, it is possible to obtain a signal in correspondence with an angular velocity for two directions intersecting at a right angle.
In this vibrating gyroscope, the excitation and detection elements may comprise piezoelectric elements having electrodes provided thereon, but the vibrating arms may themselves comprise the piezoelectric elements, and piezoelectric elements other than the vibrating arms can be used as the excitation and detection elements. That is, different constitutions of the excitation and detection elements can be realized wherein the excitation signal causes the vibrating arms to vibrate under a bending mode, and in addition, a signal in correspondence with the displacement of the vibrating arms can be output.
According to the present invention, one vibrating gyroscope is able to determine the angular velocity centered around axes in two directions. Moreover, the vibrating gyroscope can be excited using a single oscillation circuit, thereby enabling costs to be reduced to less than in conventional methods using two vibrating gyroscopes.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.